When introduced in about 1999,  the GM-100 and MapCreate combination represented a revolutionary  product in our opinion.  The ability to read detailed road maps from a CD ROM and upload only the needed map sections into the GM-100 is definitely a technology advance.   Maps furnished in MapCreate are not detailed in built up city areas as the Street Pilot, but are VERY detailed in rural areas.  City Streets maps are comparable to the level of detail in Street Atlas.  Since the quality and accuracy of the maps appear to be of great interest to users,  we will cover this area first and compare the GM-100 maps to those furnished with the Garmin G-III+ and StreetPilot.

Representative and comparative road maps for the GM-100,  G-III+, and Street Pilot can be found on our website HERE. The water detail in the Lowrance GPS maps have historically been the best available, as they are in MapCreate.  The road detail in GM-100 "base map" is quite similar to the road detail in the G-III+ and SP "base map".  While the MapCreate maps uploaded into the GM-100 are substantially more detailed than the G-III+ base maps, they appear to be from an older database.  Some major roads more than 6 years old in the Atlanta area included in the G-III+ are not shown, but most of the rural roads and streets ARE shown.  For a side-by-side comparison of the features of the G-III+ and GM-100 (Click HERE).   Note:  As with ALL OTHER consumer model GPS receivers,  ONLY maps produced by the GPS vendor can be uploaded into the GM100.  It is possible (with a good bit of effort) to use OziExplorer to edit GM100 maps and to make minor additions and changes to the GM100 maps.  (see HERE.)

Note:  Many of the rural roads and residential streets are not NAMED on the maps even when they are "pointed to" using the cursor.  Despite these limitations,  customers around the world will find the maps are very useful, and since the maps come on CD ROM,  Lowrance will have the ability to furnish updates from time to time (as with City Streets).  In order for Garmin owners to obtain maps outside the Western Hemisphere, they must purchase a second complete GPS receiver.  The opportunity for 3rd party map makers to step in and provide updated and specialty maps for downloading into the GM-100 is being fulfilled by Ozi Explorer Ver. 3.73.  Potentially, this is a great advantage.  (See OziMC examples HERE)

The feature that makes the system 'revolutionary' is the new MapCreate Software system (Win-95/98/NT 4.0 only).  This system provides the user with a CD ROM containing programs and a detailed ROAD MAP of the United States and the rest of the world to a lesser extent.  Lowrance advises that these are RURAL roads and  highways with only the major city thoroughfares  covered, not detailed city streets (as is available with StreetAtlas5/6 software or the more expensive METROGUIDE CDs of the Street Pilot.)   MapCreate provided a fairly easy method of selecting map "modules" and uploading them.  No instructions were furnished with our test copy of MapCreate, so there are probably more features than we were able to discover.

The general procedure to use MapCreate is to select the "IMS WorldMap" or the "IMS SmartMap" depending on where you live. The Help File states, "The IMS WorldMap map series data was derived from 1:1,000,000 scale base maps, and  covers the entire world between latitudes 84 degrees south to 84 degrees north, at a medium level of detail. The IMS SmartMap map series was derived from 1:100,000 scale base maps, and covers the continental U.S. and Hawaii at a high level of detail. The base maps for both the IMS WorldMap and IMS SmartMap were supplied by U.S. government agencies and conform to U.S. government accuracy standards corresponding to the map scale."  Examples of the MapCreate WorldMap can be found (HERE).

With the GPS unit connected and responding, zoom the map display to an area of interest. Apply a "connect-the-dots" outline of a proposed map and push "Create Map".  The size (in MB) of the selected area will be displayed.  If less than 1.0MB, it will fit in one of the two map partitions.  If between 1.0 and 2.0MB, it will fit itself into both map partitions. Highlight a map partition, and a simple push of the "Transfer Map" button loads the map into the GPS, overwriting any map in the selected  partitions.

We found the MapCreate maps accurate and extremely detailed and up to date in rural areas.  About twenty users from all over the USA reported generally accurate and up to date maps in their areas.   A few reports of omitted major highway segments surfaced,  but overall,  users expressed great satisfaction with the detail and quality of the map products.  However, the City Streets CD (below) has corrected this limitation.

NOTE:  NMEA must be turned off in order for the program to be installed.  The City Streets CD ($50US) contains all the maps of MapCreate plus the addition of metropolitan streets.  They are Tiger maps of an earlier date than Street Atlas 5.  For example, SA5 shows GA-400 south of I-285, but MapCreate and City Streets do not.  Other than the database date, they are exactly like SA5 maps, and of course, not as detailed as ETAK maps.  As a rough estimate, City Streets contains more than 95% of the streets and highways in the USA.  It's possible, if less detail is desired, to revert back to MapCreate maps.  The CD also contains GPS Data Manager (GDM16MS) and U.S. (marine) nav aids.  See:  HERE for a comparison of City Streets to MapCreate, Street Atlas 5, and Garmin Street Pilot maps . The CityStreets CD may contain an older version (3.1 or 3.1a) of this program which fails to work properly with some Lowrance units.  The latest version is 3.1b.

For transferring data to and from scanned and DRG map software, The GM-100 is compatible with Ozi Explorer and Fugawi, except that Fugawi can only upload tracks to Trail-1.  For transferring data to and from vector map software, the GM-100 is compatible with Precision Map 3’s GPS Links and Delorme's Street Atlas 5, 6, 7, provided the update file, deldmcgps2.exe, is downloaded from Delorme and run.

Lowrance Receivers are able to transfer data to and from Ron Henderson’s G7ToWin also supports the GM-100. With G7ToWin,  waypoints, tracks, routes, and icons can be downloaded from the Lowrance receivers to an ASCII file (for saving) or to all versions of Street Atlas.  G7ToWin also provides for uploading this data back into the GM-100 at a later time.  Downloading Screen Shots in the BMP format is another G7ToWin feature for the GM-100 and Eagle series.

Due to the cross-platform nature of G7ToWin, all data stored in Garmin hand-held receivers (or archive files) of waypoints, routes, tracks, and symbols can be uploaded to the Lowrance receivers.

It appears that the GM-100 is compatible with most moving map software programs as far as real-time TRACKING is concerned.   These include, Precision Mapping 3,  Street Atlas 5, 6, 7,  MS AutoRoute 5, Vista, NeverLost, NavMaster III, Fugawi, Ozi Explorer and others.  NMEA sentence  outputs are:  APB, GGA, GLL,  GSA,  GSV, RMB, and RMC.  (Please check our NMEA  Map  Software Compatibility list before you buy software to work with ANY low cost GPS unit.  All "NMEA 183-capable" software will not work with all "NMEA 183-capable" GPS receivers.)

First,  a review of GM-100 features, operation and specifications.  The operation and form factor of the GM-100 is the same as the Eagle series, but different from the Magellan and Garmin units.  The GM-100 is about 2.25x1.65x6.75 inches, thicker and longer as compared with the G-III+.  The case is well made and sleek in appearance.  The control buttons are small and are about twice as hard to push as on the G-III+.  The power button is  recessed to prevent accidental actuation.  The GM-100 is a comfortable  fit in the hand.   Unlike the G-III+,  one handed  operation (while holding the GM-100 in your hand) is difficult as the keyboard is located on the bottom of the unit  below  the  display.  (Note:  This is not a universally held opinion!)   The power/data connector is located  at the top rear of the case.  The  cable plug does not have a right angle cable mold, so the unit cannot be placed flat on the dash when the cable is installed.  A connection for an external antenna is provided on the rear of the unit. but the GM-100 cannot operate with commonly available external amplified antennas as the GM-100 does not provide 5v power on the antenna port

The GM-100 locks on SV signals very quickly.  From a "cold start", after a 700 mile UPS trip,  it locked on in 56 seconds.  After a 3 hour off  time,   the  lock up time was 20 seconds.  If  the  unit  is turned  off and turned back on in a few minutes  ("warm  start"),  it locks typically in about 12 seconds.  When we used the "search the  sky"  or autolocate mode,  the GM-100 took 6  minutes  to  lock.  (The G-III+  takes 16 seconds from a "warm" start  situation,  52 seconds "cold start" and 105 seconds in "autolocate" in the same environment.) Lowrance gives no specifications for start-up lock times  in  the  manual.

It is impressive that the GM-100 can lock regularly inside our homes.  No other GPS has been able to do this as consistently, including the most sensitive Garmin receiver we tested, the G-12XL 4.00.  Lowrance states the GM-100's operating temperature range is -20C to +70C; however, Lowrance  publishes no specifications for the GM-100's position accuracy.   Lowrance tells us that the GM's specification for position  accuracy  is 100 meters with SA (95% confidence).   No  accuracy  is specified  exclusive of SA  or for GM-100 accuracy with DGPS signals.  (The comparable G-III+ specs are 100 meters with SA,  15 meters exclusive of SA,  and  5 meters with suitable one meter DGPS signal. )

A comparison of the accuracy of data-logging of the Lowrance GM-100 and the Garmin G-III+ can be seen (HERE)

The GM-100 operates from 4 AA batteries or from external power in the  range  of  5 to 35 volts DC (G-III+ spec is 10 to 32 VDC.)  External current draw  is about 80ma light off and 140ma light on with +12VDC power.  On AA batteries,  the draw averages  about 180ma light off and 280ma light on 100%. ).   Battery life is not specified in the written  specifications.  Lowrance engineering suggests about 13 hours (normal mode) and 20 hours (power save mode).   (Users report an average of about 8 to 9 hours in normal mode with alkaline AA cells.)   The GM shuts down when battery voltage reaches 4.0 volts.   An optional NiMH rechargeable battery  pack is  available  with  external  charger  for  about  $100.    This rechargeable battery will be recharged INSIDE the GM-100 in two hours when  the  unit is connected to the special external charger.

NOTE:   NiCad  AA batteries inside the GM-100 will NOT be charged by the GM's  internal charger.  The battery compartment in the rear of the GM-100 is covered by a flat plastic plate.  When installing the batteries,  it can be a bit difficult to install the battery cover as the batteries tend to want to "pop out" unless you hold them.  On a couple of occasions,  the compartment cover popped open and the batteries came out unexpectedly during testing.  Though the electronics compartment is rated submersible to 2 feet,  the battery compartment is not sealed or gasketed.

The GM-100 has a memory backup battery rated to maintain data memory for ten years in the absence of AA cells.  (G-III+ battery LIFE is rated 10 years,  but the G-III+ battery will be depleted in about 3 months if AA cells are removed.)   DGPS signals in the standard RTCM-104 format are accepted.  A setup screen permits selection of the I/O combination needed by a particular application.

In the feature list below,  we have indicated (+) or (-) whenever we felt that the GM-100 feature was an improvement or not as good as the G-III+'s feature  list.  The GM-100 has an impressive  number of features  and displays that are useful.  These include:

a)   A  round  compass  type display screen (NAV mode) shows  direction  of  travel  (track) and has an arrow pointing to the  next way or routepoint.   This  screen also provides  the  absolute and relative bearing to next waypoint.  Cross track error, distance,  and ground speed,  is shown with reference to the next routepoint.   As you approach a waypoint or destination, a small circle appears on the compass screen and moves to the center  as you approach the waypoint.  This compass display  includes a "highway track" display in the center of the compass rose.  The "highway track" display page in the G-III+ is a 3-D representation of the route ahead.  Creating a Route is done by "adding" them from the map while "panning and marking", much like with the G-III+; however DELETING routpoints is much easier.  When deleting a route, the waypoints associated with it can also be deleted.  With the G-III+, deleting a route does not delete the waypoints associated with it, but with the "Detete-by-Symbol" feature, they aren't difficult to eliminate.

+b)   A  moving  map (plotter) display is provided  to  plot  your   course  over  ground.   As with the G-III+,   the  GM-100  plotter  screen  has a "base map" furnished as an integral part of the unit's firmware.  The Map display can have additional Nav information at the bottom or none.  Any  waypoints  saved in the machine are displayed on the  moving  map page as they come within range of the map scale  selected.    This  screen has pan and zoom with zoom  in/zoom  out  buttons  on  the keyboard and scales from .1  mile  to  2000 miles (or other units).  The G-III+ provides scales from 120 feet to 320 mi. (equivalent to GM-100 scales from 480 feet to 1280 miles since the GM-100 scale indicates full screen width).   A cursor control permits panning to various parts of the map plot.   Also the lat/long of the cursor crossing is shown on the display whenever the cursor is active.  The cursor is also used to place and erase icons and waypoints.   Pressing the EXIT key removes the cursor from the screen.

c)   The  map  (plotter) screen can be configured  as  North  up,   Track up,  or Course up.

d)   The  GM-100  provides a "grid lines" feature  with  the  plotter which  can  be turned on to aid in estimating  the  relative  locations of waypoints on the plotter screen.

+e)   The  GM-100  provides three separate 3000 point track trail logs.   (G-III+ one 1800 point log which can be compressed into (10) 250-point compressed logs).   The track log may be set to accumulate on a timed basis or distance-traveled basis.  Track resolution is NOT decreased when saved to one of the two saved-tracks as with the G-III+.

-f)  The GM-100 doesn't offer a third "automatic" option which plots a track point when ever the projected track deviates more than a selectable "resolution" distance as does the G-III+.  (The G-III+ offers good resolution over a  longer track with fewer track points using the automatic method.)  As with the Eagle series, the GM-100 connects un-related track plots together with unnecessary lines, which the Garmins do not.

g)   The GM-100 provides a set of twenty-eight "icons" which can be placed  to identify a waypoint.  These include an anchor,  gas pump,   airplane,  house,  fish,  etc.   Icons can be easily  placed  and removed using the cursor control.

 h)   The GM-100 has an impressive array of  "WINDOWS" that can  be selected as an alternate display.  These windows displays  include  satellite status,  NAV 1 & 2 screens,  Map 1, 2, & 3 screens, and Groups A thru J.  Map #1 is a full screen while #2 & #3 are 3/4 screens with user-selectable digital readout boxes.   Thus the maps and position data show at the same time with only a slight loss of map size as compared to the programmable window groups.  The Groups include, clock,  DGPS  status,  UP/Down timer, ETA, ETE, BRG, DST, TRK, VMG, Position,  GS,  CDI  display,  and other data in a variety of fixed arrangements.  One screen shows simultaneously your lat/long as well as your UTM position.

+i)   The GM-100 has an ALARM CLOCK function.   Unfortunately,  the GM-100 must be turned on for it to operate.    This feature will be expensive to use due to battery drain,  but the GM does have an audio alarm and some may well find this a useful feature.   No NMEA message is provided to externally enunciate an alarm.

  j)   The  GM-100  has two TIMER functions available.  A  "count down timer"  can  be set to some numbers of hours,  minutes, and seconds.   When the timer goes to zero,  an alarm  is  displayed on the screen.  There is no audible alarm.  A "count up" timer can be reset to zero and started.  It can then  be viewed to determine elapsed time.

-k)  Battery drain cannot be decreased when using the above alarms by selecting the Simulator Mode as with the Garmins.  AA battery life in the GM-100 is about half that of the G-III+.

+l)  The GM-100 has a number of Default Window Groups which display a number of parameters.  These windows can be completely configured by the user.   The GM-100 can store up to 750 waypoints.  (G-III+ = 500)

m)   Two pushes of the WPT key will automatically save your current position as the next waypoint number in the waypoint  list.   Putting in up to 8-character waypoint  names (the G-III+ only allows 6) requires a modestly involved trip through the menu system.  Naming is not as easy as in the G-III+, but is improved over the Eagle series where you had to edit out a long GPS-created name.

n)   A  feature permits you to move all information about a  waypoint from one waypoint number to another.

+o)   The GM-100 permits waypoints to be identified on the map plotter screen  in  a number of ways (or not at all).  They  may  be shown as a "number in a box",  or "named" and with or  without an icon.

+p)   The  GM-100 provides the usual ROUTE facility with a  few  additions.   99  different routes are  provided with 99 waypoints each.   One  nice addition  permits  automatic startup up in the MIDDLE  of  a  route  and  the GM-100 will select the nearest waypoint  in  the route in the direction of travel as the starting point.

  q)   Editing waypoints and routes in the GM-100 is a bit more tedious  than  with the G-III+.  There are more features  provided  for editing waypoints and some (like giving the range and  bearing between waypoints while editing routes) seem quite useful.

 r)   The  GM-100  provides a "Go to Cursor" feature.  The  cursor  is placed  on  the plotter screen at  the  desired  destination location.   Then  the "Go to Cursor" mode  is  selected  via  menus.

+s)   The GM-100 can operate with any one of 191 different map  datums  by  selecting the proper map datum from the GM-100's  map  datum  list.   (G-III+ has 107 plus user-grid datum).   The GM-100  does  have a Position Correction Factor (PCF feature)  to  permit input for offsets of an odd map datum.  UTM  is  included.

-t)   The  GM-100  does  NOT  have a user-grid datum capability which  inputs scale factor plus false northing and false easting as with most Garmins.

  u)   The GM-100 provides a Position Pinning feature which can be  set ON or OFF.  This will prevent the "wandering" position caused  by SA when you are stopped.  Although we don't use this feature in our evaluations due a possible false conclusion about the accuracy of the GPS receiver, others may find it useful and helpful.

  v)   A simulator feature provides display of simulated motion and  simultaneously outputs simulated tracking  data  to your computer for test of mapping software, data gathering  simulations and such.  Unlike the G-III,  using simulator mode to input parameter data does not reduce battery drain.

  w)   A screen back lighting timer permits setting the back  light   to 0, 15,  60, 120, 240 seconds or continuous.  The screen back lighting is continuous (when selected) on battery power.The blue-green backlit display is easy  to read at night and is an improvement on the Eagle series green screens.   Screen contrast is also adjustable  on  the  setup screen.

  x)   A  satellite  status page comes up when you first  turn  the  unit on.  It shows a "compass" display of the closest 12 satellites' numbers ( whether in view or not) along with signal strength  bars for each satellite.   The  signal-strength bars are hollow if the GPS has found the SV and  is not yet locked and changes to solid black when lock is  made  to  each  satellite in turn.  On the  polar plot,   SV  numbers are black on white when not  locked and white on black  when locked.  SV bars are listed as to the closest and not numerically as with the Garmins.  We like the fact that the GM-100 (unlike other Lowrance products) does not force the user to press "enter" to get past the "don't use this instrument as your sole means of navigation" warning.

+y)    PROJECT A WAYPOINT is available to permit a user to input a new waypoint location by entering a bearing and distance to a NEW waypoint with reference to an already existing waypoint.  The GM-100 has POSITION CORRECTION FACTOR which can be useful with unusual or uncalibrated maps.  The user can input an PCF (fudge factor) to make a known position match up with a paper map.

z)    GM-100 can operate automatically with Starlink and Magnavox DGPS receivers to automatically select and display the bit rate and frequency.  Note:  NMEA data cannot be sent to the GM while this mode is in operation.

aa) Waypoint AVERAGING is provided in the GM-100.  This allows automatic entry of a more accurate fixed position when time permits.

+bb) The GM-100 has an arrival alarm,  CDI (off track) alarm,  and an Anchor alarm.  These can be quite useful.    A Sunrise/set,  Moonrise/set calculator is included.

a)   The  DATE display is NOT automatically updated when SV  lock occurs.  The user must set the local date.  Also,  there  is no  "offset from UTC" setting.  The user must  manually  set  the  local time correct to the hour,  and minute to get  the  offset  correct.

b)  We  found that the time  display  on  our  sample  of the GM was almost exactly two seconds  slow  with  respect  to UTC from WWV.  The G-III+ display by  comparison  was about one-half second slow.  The GM has no specification  on accuracy of the time display.

We have been out testing the GM-100 on the road  and in the field.  The GM-100 has worked without a problem that either of us could find.  We had no trouble using MapCreate to upload the detailed maps we needed. We compared it with the G-III+ for lock times and  the ability to hold lock under various situations.  We  were very  impressed with the GM-100.  The GM receiver is a superior  unit and performed on a par (and sometimes better) as compared with the Garmin G-III+ (except the GM cannot use common external AMPLIFIED antennas).    We  tried  the GM-100  and the G-III+ on  the  car's  dash.

Performance was essentially equal with both units BUT we felt the receiver in our GM-100 was a bit quicker to lock than the G-III+ or the G-12XL 4.00 (the most sensitive Garmin receiver we have) and the GM-100 would occasionally achieve lock (inside a house) when the Garmins did not.   We did not note any differences in lock capability out of doors.  The simultaneous computer display tracks were essentially identical throughout  our  testing.  The GM-100  (and the G-III+) quickly  responded  to changes in direction and speed.  At about 4mph,  both units would complete  a change of direction in about 15 feet.   The  GM-100  (and the G-III+) laid down smooth tracks on our highway maps during  all tests.   No gaps, jumps, etc., were observed in the tracks except between unrelated tracks as described above.

These are the major features we have observed in working with the GM-100.   It is a well built GPS receiver and at  about  US$375,  offers good value for the money when the uploadable maps are considered.  We  liked  the  user programmable screens which give  users  an almost  totally  customized  display capability.   We  liked  the option of having digital displays of bearing,  distance and other parameters on the map plot screen.   We also liked the fact  that the  user can change the contents of these digital fields on  the plot display.

The  GM-100 gave quick lock and quality performance under all tested conditions.  The GM-100 is rated submersible to two feet of water for one minute.  Note:  The battery compartment is NOT gasketed or sealed so it should be flushed and dried out immediately if the unit is submersed.   Operating temperature range is -20C to +70C..   Storage  temperature range  is  -20C  (-4F) to +75C (+167F).  The GM-100 has  a  one  year manufacturer's limited warranty.   There  are a number of additional features in the GM-100 as compared with the G-III+ and as a result,  there are more menus to contend with.  At first,  these additional menus were a problem,  but  we quickly  learned  how they worked.  (We sometimes had difficulty finding features due to the extensive menu system.  The menus could be organized a bit better for ease of use.)  The size of the  GM-100  and G-III+ are about the same (GM-100 a bit larger)  but with slightly different form factors.  We rate the G-III slightly more of a "shirt pocket" item.  The 8.5  hour battery life of the GM-100 compared with the 18 hour battery life on the G-III+ might make the purchase of the rechargeable battery pack worth while.

We  made  these  tests using  Toshiba  laptop  computers   running  various moving  map software.  The two GPS units  were  operated simultaneously with the GM-100  on the dash in front of the driver and  with the G-III+ on the right side of the dash in front of the passenger.   The units were interchanged and no appreciable  differences in  performance were noted.  The laptops and GPS receivers were positioned so  both displays could be watched simultaneously and then we drove over a course of perhaps 30 miles and evaluated the relative performance of  the GPS equipment by observations including the  GPS  "cookie trails' on the moving map displays.

  The manual was well written and complete except for an index  and technical specifications for the GM-100.  The GM-100 "specifications"  in the  catalog are a feature list and give no quantification as  to battery drain,  position accuracy,  lock speeds,  speed accuracy,  operating temperature range,  etc.   Most of the specification information contained in this review was provided by private correspondence with representatives of Lowrance Engineering.  Users have told  us that service  for the GM-100 is fast and reasonably priced.   The major complaint is that the GM-100 is in high demand and difficult to find for purchase -which is an indication of the level of demand for this receiver..

  We appreciate the assistance of Lowrance Engineering personnel with questions and specification data not available in the manual.

Users had generally favorable remarks with respect to the GM-100.  Here are a few items which were repeated.

1)     Screen scratches easily and needs protection.
2)     Battery compartment cover is flimsy and pops off unexpectedly at times.  Batteries are clumsy to install.
3)     MapCreate's maps often seem to either lack detail or are too cluttered depending on zoom level.  Zoom should maintain a relatively constant level of detail on the screen.  (I concur,  but think this will be corrected in future updates.)
4)     No power provision for use with commonly available external antennas.
5)     Case is too "fat" for shirt pocket convenience and screen cannot be rotated.

OVERALL,  the respondents had a very positive response and were especially pleased with the downloadable map capabilities and general feature arrangement provided with the GM-100.  Good quality  of technical support was mentioned by several users.

If  anyone  has any additions,  questions,   suggestions,   error corrections or other comments,  please feel free to Email:

Joe Mehaffey or Jack Yeazel

GOOD NAVIGATING